Tag Archives: welded joints
The article is devoted to the issues of safety provision during gas consumption and gas distribution in cities and residential areas. The performed analysis of the literature showed that significant part of the pipelines transporting gas to the residential areas is applied for operation for more than 40 years. The dependency of the number of accidents of gas supplying and gas distributing networks on the increase of the total length of the network determined on the basis of Rostekhnadzor of RF data shows the tendency of emergency situations increase. On the one hand this is connected with the increase of the service life of the pipelines and accumulation of damages in the pipelines material. Moreover, it was found out that control of the residential buildings networks is not under the supervision of the regulatory authorities due to the amendment of norms and regulations in the field of industrial safety.
Due to the fact that operation of gas distribution systems is performed in the quasi-static mode of loading, these facilities do not considered from the point of view of accumulation of damages in the gas pipelines material and there is no applicable regulations regarding its safety operation period. However, from the literary sources it is well known that complex processes occur in the material on micro and macro levels during the operation period of the equipment. This causes accumulation of damages, locally obtaining limiting state, and creates the possibility of brittle failure in case of an emergency situation.
Carried out research showed that thermal expansion distribution coefficient in the area of welded joint of the material of the gas pipelined made of steel 20 is unstable. This means that stress appeared in the result of the strength load is also distributed irregularly. In the result, accumulation of damages in the areas with the increased stress, which locally could achieve the yield limit, occurs faster.
The article describes the possibility of application of nondestructive method of evaluation of the stress state in the welded joints of the gas pipelines which could provide the possibility to register the rate of accumulated damages in the potentially hazardous elements of the gas distribution systems.
Influence of deformation on mechanical properties of 20 and 30HGSA steel welded joints in superplasticity regime
It may prove to be promising to use hot plastic deformation of welded joints in temperature/velocity regimes of metal superplacticity effect revealed, in order to get structural homogeneity and combination of high strength and plasticity. Isothermal rolling with hot rolls of 20 and 30HGSA steel weld joint specimens was carried out at 10, 20 and 40% deformation degrees at a temperature of 730 ± 5 ºС being the optimal temperature of superplastic deformation for constructional steels, at a constant strain rate of 0.003 s-1. The rolling was performed in the laboratory six-high LIS-6/200 mill of the Institute for Metals Superplasticity Problems, Russian Academy of Sciences, with isothermal deformation conditions being provided by heating the working rolls and regulating their temperature. The minimum difference in the weld joint base metal ultimate strength values compared to the initial state is observed at 20% deformation degree and is equal to 6.3% for 20 steel and 5.2% for 30HGSA steel. The minimum difference in the weld joint base metal yield point values compared to the initial state is also observed at 20% deformation degree and is equal to 6.0% for 20 steel and 4.6% for 30HGSA steel. It is shown that isothermal rolling with hot rolls in superplastic deformation regime results in reduction of scattering of mechanical properties in different zones of 20 and 30HGSA constructional steel welded joint compared to the initial state. The comparative analysis of micro hardness and hardness values of the welded 20 and 30HGSA steel specimens after different kinds of welding treatment with equal time spent on the treatment showed that the rolling with isothermal rolls in superplastic deformation regime with 20% degree of strain has an advantage in achieving homogeneity of mechanical properties compared to annealing and thermal cycling treatment.
The estimation of durability and safety of operation of the welded technological pipeline from a steel 17G1SU in diameter 400 mm with thickness of a wall of 10 mm, loaded with internal pressure 6 МPа, intended for transportation of oil products is made. Dependence of change of limiting bearing ability of the pipeline on operation time in an excited environment is established. Calculation of pressure in a real design with the revealed not through defects is essentially specified. The expediency of application of diagrams of an indestructibility is proved at an estimation of resource characteristics and survivability of the welded equipment from low-alloy steels.